From: slash.tmp@free•fr (Mason)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arm: spin one more cycle in timer-based delays
Date: Tue, 15 Nov 2016 14:36:33 +0100 [thread overview]
Message-ID: <582B0F61.6030903@free.fr> (raw)
When polling a tick counter in a busy loop, one might sample the
counter just *before* it is updated, and then again just *after*
it is updated. In that case, while mathematically v2-v1 equals 1,
only epsilon has really passed.
So, if a caller requests an N-cycle delay, we spin until v2-v1
is strictly greater than N to avoid these random corner cases.
Signed-off-by: Mason <slash.tmp@free•fr>
---
arch/arm/lib/delay.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index 69aad80a3af4..3f1cd15ca102 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -60,7 +60,7 @@ static void __timer_delay(unsigned long cycles)
{
cycles_t start = get_cycles();
- while ((get_cycles() - start) < cycles)
+ while ((get_cycles() - start) <= cycles)
cpu_relax();
}
--
2.9.0
next reply other threads:[~2016-11-15 13:36 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-15 13:36 Mason [this message]
2016-11-18 12:06 ` [PATCH] arm: spin one more cycle in timer-based delays Will Deacon
2016-11-18 12:24 ` Mason
2016-11-18 12:54 ` Russell King - ARM Linux
2016-11-18 14:18 ` Mason
2016-11-18 14:42 ` Peter Zijlstra
2016-11-18 17:51 ` Mason
2016-11-19 7:17 ` Afzal Mohammed
2016-11-19 11:03 ` Russell King - ARM Linux
2016-11-19 18:29 ` Mason
2016-11-20 19:18 ` Doug Anderson
2016-11-20 19:44 ` Russell King - ARM Linux
2016-11-20 20:00 ` Mason
2016-11-20 6:15 ` Afzal Mohammed
2016-11-20 19:15 ` Doug Anderson
2016-11-18 17:13 ` Doug Anderson
2016-11-18 17:32 ` Russell King - ARM Linux
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